Method of making hollow propellers



Feb. 23, 1943- G. D. WELTY METHOD OF MAKING HOLLOW PROPELLERS Filed July 25, 1939 2 Sheets-Sheet l llu -lrlrll QJ Q Q Q as .& m H i. ii. m P I i! II} I m p N P QM Geo ge 0. Wlig wan/ Feb. 23, 1943. G. D.-,WELTY METHOD OF MAKING HOLLOW PROPELLERS Filed July 25; 1959 2 Sheets-She e-t' 2' W m/ A ORNEY w- $5 Q Mk INVENTOR j George D Welly BY @fl-m gill Patented Feb. 23, 1943 METHOD OF MAKING HOLLOW PROPELLERS George Donald welty, Shaker Heights, Ohio, as-

signor to Aluminum Company of America,

Pittsburgh, Pa, a corporation of Pennsylvania Application July 25, 1939, Serial No. 286,397

4 Claims. (Cl. 29-1563) This invention relates to a method of forming hollow metallic articles, and more particularly to a method of forming hollow metallic propeller blades for aircraft.

Many aircraft propeller blades have heretofore been made of'aluminum or other light metal alloy stock. The most successful metal airplane propeller blades heretofore made have been those made of light metal alloys and fabricated in accordance with U. S. Patents Nos. 1,957,499, 2,044,-

293, 2,044,294, and 2,044,295. Many efforts have been made, however, to further reduce the weight of the propeller blades in proportion to their length and airfoil section without sacrificing the necessary strength to carry the various centrifugal, thrust and vibratory loads to which the blades are subjected.

A reduction of the weight'of metal propeller blades in proportion to their size while maintaining the necessary strength, durability, fatigue resistance, and uniformity has been accomplished propeller blank Lduring the forming operation,

thereby causing the wall to conform to the contour of forming. dies.

In connection with my invention a blank is preferably formed, from a billet which has been rolled or extruded, and is first tapered towards the end which will eventually be the tip end of the propeller blade. In this tapering operation at least a portion ofthe billet is given a roughly conica1\ shape, with the small end at the endwhich will form the tip of the blade and with sufficient cross-section of metal throughout the by designing and making blades in accordance with the following method. This method consists essentially in forming a blank tapering generally from the end which is to form the hub to the end which is to form the tip. of the blade, and having sufllcient cross-sectional area at each point in its length to provide the necessary metal for the thin walls of the blank are not properly supported .when the pressure of the forming tool is applied to the hollow blank, there is a tendency for the walls to collapse or otherwise not conform to the contour ofthe dies. A number of methods of giving internal support to the walls of hollow propeller blanks have been proposed in the art at various times but nonehas proved entirely satisfactory.

The principal objectof the present invention is to provide a method of forming hollow metallic articles in which internal support is given to the blank during the forming operation. I Another object of my invention is to provide a. 'method of givinginternal support to the walls of a hollow 4 finished blade, and then forging or pressing the length of the tapered portion to form the corresponding cross-section of the finished blade. Preferably a substantial length of the billet isleft unworked in this operation, and this portion ultimately becomes the shank and hub end of the blade. The tapering operation may be performed in any 'way so far as the present invention is con- A 7 cerned. either by machining or mechanical deformation, Preferably, however, it is performed by rolling in accordance with the process disclosed and claimed in U. S. Patent No. 2,044,293.

The tapered billet is next mechanically deformed so as toprovide earsor fins disposed longitudinally along the tapered portionfwhich fins ultimately become the leading and trailing edges of the propeller blade, and an internal hole'or recess is formed throughout the major portion of the length of the blank, either by piercing or boring, or suitable combination of such operations. The hole is preferably substantially circular in cross-section and taperstowards the tip end of the blank. The non-circular external contour of the blank and the round hole in the blank com l bine to provide non-uniform walls so that the stresses may be distributed in accordance with the eventual loads to which the blade is sub- Jected.

The shank end of the hollow blank may be made of greater diameter than is ultimately necessary or desirable with the particular blade size so that the internal openins'may be made of uniform diameter through the shank and into the blade portion. The shank endof the blank is then swaged or otherwise worked to reduce its diameter and increase the wall thickness while maintaining approximately a circular cross-section. The shank end is thereby brought to the desired size with respect to the blade portion while retaining sufiicient wall thickness to adequately carry the centrifugal and bending loads to which it is subjected. This operationalso works the shank and hub portions of the blank which would be left unworked by the later forming steps, thereing, or swaging.

by making the amount of working more uniform throughout. Th shank end of the blank is preferably machined inside and out to bring it substantially'to the rough finished dimensions and true up the outside and inside surfaces which may be distorted by the swaging operation. Preferably'before the final shaping of the blank, a flange the general contour of the exterior walls but provide a non-uniform wall thickness designed to compensate for unequal distribution of stress when the propeller is in operation.

,My invention resides in the manner by which the internal walls of the hollow propeller blank are supported during the forming operations. A core of a relatively low melting point metal, such as lead, is cast in the aperture of a hollow propeller blank, provided as described in the pre-' ceding paragraphs, in such a manner that it contacts opposite internal walls and forms a partition-like support extending the entire length of the hole. In forming this core a pattern of the siZe and shape of the core is first inserted into the hollow blank. Since the opening through the shank is preferably somewhat smaller than the central portion of the hole, the pattern is preferably composed of a number of longitudinal sections which may be inserted separately. The pattern when inserted inthe blank forms'a partition-like member contacting two opposite walls and extending the full length of the recess in the blank. The space existing on either side of the pattern is thereafter filled through the shank opening with a suitable molding sand. The pattern is then withdrawn and a metal of suitable properties is cast into the' mold left by the pattern. When this metal core has .had suflicient time to cool, the sand is removed leaving an unoccupied space of p're-calculated volume on either side of the core, which space will be substantially taken up during the forming operation. The core, while in this partition-like position forms a rigid support which gives suflicient resistance to the pressure of the forming dies to prevent the walls of the blank from collapsing or otherwise not conforming to the contour of the dies. As the forming operation proceeds, the core, in giving support to the internal walls of the propeller blank, is deformed and compressed until the space that originally existed on either side of the core is substantially taken up. Thecubic content of the metal comprising the core is calculated to exactly occupy the hole in the rough formed propeller blade.

. When this condition is reached, the metal which comprised the core is removed and the blade is trimmed and machined to final dimensions.

My invention may be more clearly understood Fig. 10;

ears or fins and the formation of the hole inthe blank;

Figs. 4,- 5, and 6 are cross-sections taken on th lines 4-4, 55, and 66, respectively, of Fig. 3;

Fig. 7 is a side view partly in section of the blank after the shank portion has been swaged and a hub flange formed thereon;

Fig. 8 is a side elevational view illustrating a multi-piece pattern suitable for use in my inven-f tion, showing the various pieces thereof sepa rated;

Fig. 9 is a plan view of the pattern;

Fig. 10 is a vertical section taken centrally and I longitudinally of a pair of dies and a propeller blank in position for the forming operation and showing the cast core in the blank;'

Fig. 11 is a view taken on the line ll-ll of Fig. 12 is a planview of the rough finished blade; and

Figs. 13 to 20, inclusive, are views on an enlarged scale taken on lines |3l3 to -20, inclusive, respectively, of Fig. 12.

Referring to the drawings, the specific embodiment of my invention illustrated herein preferably starts with a billet of aluminum alloy. As illustrated in Fig. 1, this billet is substantially circular in cross-section, although it will be understood that it may be elliptical or of other shape. For.c0nvenience in handling during the initial operations, .the billet may be provided with a tong hold I, as shown.

The major portion of the billet remote from the tong hold is first tapered or' coned to elongate the billet to the desired blade length and prov ide suitable cross-section of metal for the 'formation of the blade at different points through- :out its length. The blank then consists of the ing, rolling, or in any other suitable manner.

Preferably the fins are arranged to spiral a slight amount about the blank, as indicated in Figs. 4 to 7, in a rough approximation of the relative spiraling or pitch of the finished blade.

by referringto the accompanying drawings which I illustrate diagrammatically the various steps comprising one mode by which my invention may be practiced.

Fig. l is aperspective view of a billet suitable for use in forming a propeller blade;

Fig. 2 is a perspective view of the billet after the tapering operation.

Fig; 3 is a plan viewpartly in section of the 'blank after the formation of laterally-projecting The fin 4 is designed to form the trailing edge of the blade, and the fin 5 is designed to form the leading edge. Preferably the fin l is made of a slightly greateriateral extent and a slightly less thickness than the fin 5 to provide the necessary metal and arrangement thereof to form the leading and trailing edges in the finished blade.

The blank is then formed with an internalhole or recess by boring a substantially cylindrical aperture through the shank 3 of the blank and through the greater portion of the length of the tapered portion 2 and terminating it in a substantially conical portion 8 which stops short of the tip end of the blade, as shown in Fig. 3. It willbe understood that the internal hole may be made in otherwise worked, thereby reducing its diameter and increasing itswall thickness to the desired extent. The shank portion 3 of the blade is then machined inside andsout to desired rough finish dimensions, and inthis operation any inaccutacies in the contour and thickness of the shank end produced by the swaging operation are removed. The shank end is preferably upset at this stage of the process to form a flange II on the hub end. At the conclusionof the swaging and upsetting operation the blank has the form illustrated in Fig. '7, with the hollow substantially cylindrical shank/flaring into the ribbed blade portion.

The blank is now ready for the specific application of my invention. A multi-piece pattern, designed to conform to the longitudinal contour of the internal walls of the blank when assembled, is inserted in the hole in the hollow blank.' In

/the embodiment shown in Figs. 8 and 9, the pattern, preferably of wood, consists of three separate sections. Nevertheless a larger or smaller number of sections may serve equally as well, providing'the sections are so designed as to permit them to be inserted through the shank opening. Either section II or ii of the pattern is inserted in the blank through the shank opening, the curved portion following the longitudinal contour of the internalwalls and extending nearly the full length of the hole leaving only a small area in the tip {or the end'of the central section of the pattern. After either one of the curved sections l3 or I! is inserted in its proper place, the corresponding section is inserted in the same relative position along the opposite internal wall. These sections, contacting opposite walls of the blank, are held in place by inserting the central section M of the pattern. The sections of the p'attem are tongued and grooved, as shown at IS in Fig. 8, thereby permitting each section to align on a common plane with the adjacent sections. When the pattern is inserted in the hole as just described, it forms a partition-like member extending substantially the full length of the hole in the blank and contacting opposite sides thereof, leaving an unoccupied space on either side. This unoccupied space is 49 filled through the shank opening with suitable molding sand in the same manner commonly em} ployed for ramming up molds prior to casting metal. The multi-piece pattern is then withdrawn by first removing the central section ll and then the two curved sections l3 and I5. Each piece of the pattern may be provided with a tong hold I! to facilitate'handling thereof.

The cavity vacated by the pattern is then filled with molten metal through the shank opening. In pouring the molten metal into the mold considerable care is required in order not to injure the sand mold which remains after the pattern is withdrawn. In most instances, the core may easily be poured by laying the propeller blankin nearly horizontal position-slightly elevating the shank end. As the molten metal is poured slowly through the shank opening, the shank end of the blank is gradually raised until the blank is in nearly a vertical position with the shank end at the top, at which time the mold will be full of molten metal. The core may be of any metal having a melting point suificiently below the meltingpoint of the metal comprising the propeller blade to permit melting of the core without injury to the propeller blade, yet high enough to remain solid during the forming operation; the material should also have suflicient strength under compression to give adequate support to the internal walls of the'blank at working temperatures, and suflicient ductility to permit deformation beneath the forming dies. For example, when the blank is of aluminum or aluminum base alloy, a lead or lead alloy'mandrel is satisfactory.

When the core has solidified and cooled, the sand is removed from the blank through the shank openihg by any suitable means, leaving a partition-like metal core I. in contact with opposite internal walls of the blank, as shown in and 11.

Figs. 10

The propeller blank containing the metallic core is then inserted between forming dies, with the supported sides of the blank in a position to 1 contact} the forming dies first. as illustrated in is increased, until at the finish of the operation the hole in the blade is substantially completely filled with the metal which originally comprised the core. The cubic content'of the core can be made equal to the desiredcubic content of the hole in the rough finished blade by controlling v the original dimensionsof the core.

When the forming operation iscompleted, the rough formed blade containing the deformed coreis removed from the dies and heated to a temperature sufllciently high to melt the low melting point metal which originally comprised the core, but not to a temperature high enough to injure the. metal comprising the blade. The blade is held at this temperature sufiiciently long to permit all the low melting point metal to melt and run from the blade. The method of working the" blank to blade shape as just described may be varied in detail without departing from the spirit of the invening of the hollow propeller blade, as for instance,

forging, pressing, or rolling operations.

Following the operations described, the formed blade is completed in any desired way, usually by trimming, sizing, and heat treating. The blade may then be given a finishing operation, such as machining, grinding, and polishing to bring it'to the exact dimensions and surface characteristics gesired, and is then ready to be mounted. in a While I find this invention to be most useful in the manufacture of blades from aluminum alloy or other light metal alloy, it is also readily adaptable to the manufacture of blades from other metals. The core used in forming the blade should be of a metal having a melting point below the melting point of the blade yet above the working temperature. For example, a core of copper may be employed in making blades oi' iron or steel; an aluminum core may be employed in making blades of copper and its alloys, suchas brass and bronze; and an iron or copper care may be employed in making hollow blades of nickel. In fact, any metal that can be forged or rolled may be worked by this process.

Although I have described a specific example of my invention, it will be understood that many variations and rearrangements of the steps may be resorted to without departingi'rom the scope of the invention.

I claim:

1. A process of producing hollow metallic propeller blades comprising the steps of forming an elongated metal blank having a hole therein, casting into said hole a core of a metal having a melting point below the melting point ofthe metal of the blank, said core forming a celitrally disposed partition in said blank extending in contact with opposing portions of said blank substantially the entire length of said hole, work-forming said blank and said core by applying pressure to the portions of said blank supported by said core until the core substantially illls the hole in the blank, said core yieldingly supporting said blank internally during substantially the entire work-forming operation and being adapted to be work-formed by-the workforming operation at least as readily as saidblank, and thereafter removing the core metal from said blank.

2. A process of producing hollow metallic pro-' peller blades comprising the steps of forming an elongated metal blank having a hole therein,

' casting into said hole a core extending between opposing portions of said blank for substantially the entire length of the hole and forming a centrally disposed partition therein, said core havi ing a melting point below the melting point of the metal of the blank and having a cubic content smaller than the cubic content of said hole, work-forming said blank and said core by applying pressure to'opposing portions of said blank supported by said core until the core substancasting into said hole a core extending between opposing portions 0! said blank and forming a centrally "disposed partition herein, said core having a melting point below the melting point of the metal of the blank and having a cubic content smaller than the cubic content of said hole, work-forming said blank and said core by applying pressure to the portions of the blank supported by said core until the core substantially fills the hole inthe blank, said core yieldingly supporting said blank internally during substantially the entire work-forming operation andbeing adapted to be work-formed by the work-forming operation at least as readily as said blank, and thereafter removing the, core metal from the blank. 7

4. A process of producing hollow metallic .propeller blades comprising the steps of forming an elongated metal blank having a hole therein, introducing into said hole a metal core extending between opposing portions of said blank and forming a centrally disposed partition therein to lend effective continuing support to opposed work-formed areas of the blank in subsequent work-forming of the blank, work-forming said blank and said core by applying pressure to said opposing portions of the blank supported by said core until the core substantially fills said hole, said core being adapted to be work-formed by the work-forming operation'at least as readily'as said blank, and thereafter removing the core metal from said blank.

GEORGE DONALD WELTY. 

